Wave surface characterization

ABSTRACT

A method of obtaining data for mathematical characterization of a wave surface by transmitting a beam toward the surface so that the beam is reflected from an element of the surface in a direction determined by the instantaneous, two dimensional slope of the element. The reflected beam impinges on a screen as a spot whose time varying coordinates correspond to the time varying slope of the element. These coordinates are captured by scanning the screen with a raster scan which controls counters identifying the spot position. The instantaneous distance is measured by a capacitance probe to relate the captured coordinates to the corresponding angles of reflection by appropriate trigonometric relations.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention pertains to the field of optical measuring and testing,more particularly to the measurement of angles in two planes todetermine the two dimensional slope of a wave surface.

2. Description of the Prior Art

It is known to detect the presence or passage of a wave or wave on asurface by apparatus detecting a change in the angle of a beam reflectedfrom the surface or a change in the gross reflectance of the surface.

However, it is often desirable to distinguish a direct reflection oremission from an object from a simultaneously received indirectreflection via a time changing wave surface. If the time changingsurface can be mathematically characterized, the direct transmission canbe distinguished from the indirect reflection from the wave surface.

SUMMARY OF THE INVENTION

The present invention involves mathematical characterization of a wavesurface by transmitting a beam toward the surface so that the beam isreflected from an element of the surface in a direction determined bythe instantaneous, two dimensional slope of the element. The reflectedbeam impinges on a screen as a spot whose time varying coordinatescorrespond to the time varying slope of the element. These coordinatesare, typically, captured by scanning the screen with a raster scan whichcontrols counters identifying the spot position. Where the distance fromthe screen to the surface varies with time, the instantaneous distanceis measured to relate the captured coordinates to the correspondingangles of reflection.

It is an object of the present invention to characterize a wave surfaceby the time varying, two dimensional slope of an element of the surface.

Another object is to provide a method and apparatus for continuouslydetermining the time varying slope of an element of a wave surface.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, advantages, and novel features of the subject inventionwill be apparent from the following detailed description when consideredwith the accompanying drawings in which:

FIG. 1 is a schematic view of apparatus and operating environment of thesubject invention;

FIG. 2 is a block diagram of a wave computer of the apparatus.

DESCRIPTION AND OPERATION OF THE PREFERRED EMBODIMENT

FIG. 1 depicts an apparatus 10 for use in carrying out the method of thesubject invention. Apparatus 10 is shown in an operating environmentwhich includes a wave surface 12, such as the sea surface, having aninfinitesimal plane element 13 whose time varying, two dimensional slopecharacterizes the surface and is obtained by apparatus 10 for,typically, preservation by a recorder 15 and analysis by a computer 16.

Apparatus 10 and element 13 are associated with a three dimensionalcoordinate system identified by numeral 18. In this system the X and Yaxes are in a horizontal plane generally parallel to surface 12, the Zaxis is vertical, and the instantaneous, two dimensional slope ofelement 13 is identified by angles phi (φ) and theta (θ), where phi isthe angle between the Z axis and the unit normal to element 13 and wheretheta is the angle between the X axis and the projection in the X-Yplane of this normal on said plane.

Apparatus 10 includes a translucent, planar screen 20 disposed parallelto the X and Y axes above element 13 and spaced therefrom any suitabledistance. The apparatus includes a laser 22 at one side of screen 20 andincludes a mirror 24 centrally of and below the screen. Laser 22 istypically a helium-neon laser which emits a beam 25 reflectable fromsurface 12. Laser 22 and mirror 24 are disposed so that beam 25 isreflected from the mirror parallel to the Z axis along a first path 26toward surface 12. Beam 25 is reflected from surface 12 along a secondpath 27 determined by angles phi and theta. Path 27 impinges on screen20 as an illuminated position or spot 29. The instantaneous coordinatesof spot 29 on screen 20 are indicated by "x" and "y" and are determinedby the two dimensional angular relations between paths 26 and 27, theangle between these paths being twice phi due to the law of reflection.

Apparatus 10 has a well-known capacitance probe 30 extended along the Zaxis from screen 20 surface 12 at a location as close as practical toelement 13, the position of this element on the surface being determinedby the intersection of path 26 with the surface. The capacitance ofprobe 30 varies linearly with the relative immersion of the probe in theliquid which bears surface 12 so that the probe measures, as describedlater, an instantaneous distance "z" between screen 20 and element 13.

Apparatus 10 includes a well known video camera 32 disposed above screen20 to perform a raster scan thereof along the X and Y axes and to detectat each scan period the instantaneous position of spot 29 on the screenand thereby measure coordinates x and y.

Apparatus 10 incorporates a wave computer indicated in FIG. 1 by thenumeral 35 and configured internally as shown in FIG. 2. Computer 35 isconnected to probe 30 by connection 36 and receives a video signal fromcamera 32 by a connection 37. Computer 35 has a ground connection 38,shown only in FIG. 2, for use with probe 30. Wave computer 35 typicallyprovides a vertical sync signal to analysis computer 16 by a connector39. Computer 35 determines instantaneous coordinates x, y, and z in amanner shortly to be described and provides these coordinates,respectively, via connections 41, 42, and 43 to recorder 15 and toanalysis computer 16.

Wave computer 35 may be configured in various ways apparent to oneskilled in the art to convert the signals received from connections 36and 37 to appropriate signals on connections 39 and 41 through 43, theparticular configuration depending on the relative magnitude andfrequency components of the waves of surface 12 and whether digital oranalog signals, or both, are to be supplied to recorder 15 and computer16. The configuration now to be described is believed especially suitedfor use with sea surface waves and with a standard composite videosignal from camera 32.

As shown in FIG. 2, computer 35 has a sync stripper 50 which receivescomposite video signal 37 and outputs a horizontal sync signal 51 and avertical sync signal 52, signal 52 being output from computer 35 byconnector 39. Signal 37 is also received by a threshold detector 55which outputs a signal to set a flip-flop 56 reset by signal 52. Theoutput of flip-flop 56 is a lock signal 57.

As indicated by numeral 60, computer 35 has a 16 MHz clock divided by 4to provide an X clock signal 61 and divided by 1050 to provide a Y clocksignal 62. Computer 35 has an X counter 65 driven by signal 61 and resetby signal 51 and has a Y counter 66 driven by signal 62 and reset bysignal 52. The counts of counters 65 and 66 are received, respectively,by latches 68 and 69 which accept the corresponding count when signal 57is asserted. The content of latch 68 is output on connector 41 and thecontent of latch 69 is output on connector 42. Computer 35 thuscaptures, at each video field and in latches 68 and 69, countscorresponding to the coordinates x and y on screen 20 of spot 29.

Wave computer 35 has a pulse width modulation one-shot 70 reset by a 10KHz clock 71. After each reset, one-shot 70 is set after a timedetermined by the capacitance of probe 30 across connections 36 and 38to one-shot 70. The resulting pulses are summed and filtered by anintegrator 73 whose output is provided through an analog to digitalconverter 74 to a Z latch 75 which is clocked by signal 57 and providesto connector 43 a digital signal corresponding to coordinate z at themoment each video frame when x and y are captured.

When the coordinates x, y, and z are obtained each video frame time byapparatus 10, the two dimensional slope of element 13 represented by phiand theta at each such time may be calculated by the followingtrigonometric relations. ##EQU1##

Successive time varying such slopes may be analyzed in any suitablemanner, as by Fourier analysis, to mathematically characterize wavesurface 12.

Obviously, many modifications and variations of the present inventionare possible in light of the above teachings. It is, therefore, to beunderstood that the invention may be practiced within the scope of thefollowing claims other than as specifically described herein.

What is claimed is:
 1. A method of characterizing a time varying wavesurface, comprising:directing a beam reflectable by said surface along apredetermined first path toward said surface so that the beam isreflected from an element of said surface along a second path determinedby the instantaneous two dimensional slope of said element; determiningthe two dimensional angular relation between said paths; and calculatingsaid slope from said angular relation.
 2. The method of claim 1 whereinsaid angular relation is determined by:disposing a screen in said secondpath so that the reflected beam impinges on the screen; scanning thescreen by a scan in a first dimension and in a second dimension toidentify, by a pair of coordinates corresponding to said dimensions, aposition on the screen at which the reflected beam impinges; measuringanother coordinate from the screen to said element along a thirddimension therebetween; and calculating said two dimensional slope bytrigonometric relations between said coordinates.
 3. The method of claim2 wherein:said screen is translucent to said beam and said position isan illuminated spot thereon; and said scan is performed by a rasterscanning device sensitive to said spot and disposed oppositely of thescreen from the surface.
 4. The method of claim 2 wherein:said surfaceis liquid surface and the distance along said third dimension betweenthe screen and said surface is time varying; and said another coordinateis measured by a probe extended from the screen through said surface.